An air conditioning system for a vehicle is generally constructed to regulate a room temperature by a refrigeration cycle for circulating a refrigerant. The air conditioning system of this kind is disclosed in Japanese Patent Laid-open No. 2000-142078. According to an air conditioning system for a vehicle disclosed in the Laid-open, a compressor, a condenser, a receiver, an expansion valve, an evaporator and so on are arranged in a circulating circuit of the refrigerant. In a casing of the air conditioning system, a blower fan and an evaporator are arranged. Moreover, an air inlet and an air outlet are formed on the casing.
Here will be explained an operation example according to the aforementioned air conditioning system. First of all, when the blower fan is driven, air is inhaled from the air inlet into the casing. On the other hand, when the compressor is driven by an engine power, the refrigerant is compressed by the compressor and made into a high-pressure refrigerant. The compressed and high-pressured refrigerant is then condensed by the condenser and passes through the receiver. The refrigerant is consequently made into a high-temperature and high-pressure liquid refrigerant. This liquid refrigerant is expanded by the expansion valve, and conveyed to the evaporator in the form of a low-temperature and low-pressure liquid refrigerant. In the evaporator, heat in the air is transferred to the refrigerant due to the temperature difference between the air in the casing and the refrigerant, thereby evaporating the liquid refrigerant. The low-temperatured (cooled) air is then fed from the discharging port to the vehicular room. The refrigerant passed through the evaporator flows into the compressor again. Thus, the temperature is regulated in the vehicular room.
“Flow rate of refrigerant” is any one of the conditions which affect the heat transferring capacity of the refrigerant in the circuit. According to the air conditioning system disclosed in the aforementioned Laid-open, since the compressor is driven to transport the refrigerant, the air conditioning function thereof is easily affected by the operating condition of the compressor. This makes it probable that necessary air conditioning function cannot be obtained.